1. Field of the Invention:
This invention relates to an improved wiper blade rubber having a small sliding resistance and a method producing the same.
2. Description of the Prior Art:
A wiper blade rubber comprises a rod-shaped base portion and a sliding portion provided with a lip in the form of a thin plate. The wiper blade rubber has an elongated form and it is used for a rubbing member of a wiper. Thus, the wiper blade rubber is of a sliding member to wipe up or remove water from the surface of such as a front glass of an automobile.
Conventionally, this blade rubber has been made of rubber to utilize the flexibility thereof. The wiper blade rubber is slid along the surface of a glass thereby to wipe up water therefrom.
In this case, there is such an advantage that the wiper blade rubber has flexibility, because the component of which is rubber. However, there is also such a contrary disadvantage that the wiper blade rubber has a large sliding resistance.
So, in order to produce a rubber sliding member having a small sliding resistance, for example, the following prior method has been proposed.
Namely, a lubricative fine power, such as graphite, molybdenum disulfide, fluroplastic in the form of powder or the like, is added to an elastomer binder containing a vulcanization agent and mixed by a roll mill or a banbury mixer. (Hereinafter, the aforesaid lubricative fine powder may be called "a lubricant".) Then, the resulting mixture is formed into a sheet by using a calendar roll or the like and the sheet is placed on a non-vulcanized product body. And then, the elastomer binder and elastomer product are vulcanized in one body by heating and pressing them thereby to form a sliding layer on the elastomer product body.
In this prior method, however, it is required to use a large amount of elastomer binder relative to that of lubricant to be used (e.g., the amount thereof being more than 2.5 times the amount of lubricant in the normal volume ratio), because a roll mill, banbury mixer, calender roll or the like must be used in the aforesaid steps. Therefore, the amount of lubricant contained in the formed sliding layer becomes relatively small. As a result, the sliding layer thus formed has little effect in reducing a coefficient of friction of the layer. Moreover, the aforesaid apparatuses, such as a roll mill and mixers, are required for mixing the lubricant with the elastomer binder. Thus, in the prior method, it has not been necessarily easy to form the sliding layer.
Furthermore, according to this prior method, it has also been difficult to form such a sliding surface layer having an entirely uniform thickness on such a thin lip of wiper blade rubber as the thickness thereof is about 0.6 to 1.0 mm. Namely, there have been encountered such disadvantages that the formed sliding layer is too thick, or the lip cracks, or otherwise the sliding layer can not be partially formed on the lip.
On the other hand, in order to reduce the sliding resistance of the wiper blade rubber, other prior methods have been also known.
For example, the surface of the wiper blade rubber is chlorinated to harden the surface thereof. More particularily, firstly, a wiper blade rubber is produced and thereafter, it is chlorinated to harden the surface thereof thereby to reduce the sliding resistance thereof.
Or, there is formed on the surface of the wiper blade rubber a coating layer comprising a lubricant such as molybdenum disulfide powder or the like to reduce the sliding resistance thereof by the coated film of lubricant.
However, the former chlorinating method has poor effect on reducing the sliding resistance of the wiper blade rubber. And also, it can be used only in the case of rubber containing diene groups.
Whereas, according to the latter method, the coating layer formed on the wiper blade rubber comes off from the surface thereof and wears in a short use thereof and therefore, the coating layer formed by the latter method has poor durability.
Accordingly,in the aforesaid prior art, a wiper blade rubber having an excellent durability as well as a small sliding resistance has not been proposed.